The present invention relates to fluidized beds and, more particularly, to a fluidized bed heat exchanger in which a baffle system is provided for separating the entrained particulate bed material from the discharging air and gaseous products of combustion.
The use of fluidized beds has been recognized as an attractive means of generating heat. In these arrangements, air is passed through a bed of particulate material, which normally consists of a mixture of inert material and a fossil fuel such as coal, to fluidize the bed and to promote the combustion of the fuel. When the fluidized bed system is utilized as a steam generator, a boiler, a gasifier, or the like, it offers an attractive combination of high heat release, improved heat transfer to surfaces within the bed, and compact size.
In all fluidized bed reaction processes unreacted or partly reacted particles are entrained by the air and gaseous products of combustion passing upwardly from the bed and escape into an area immediately above the bed commonly referred to as a "freeboard space." In a majority of these type of designs, the height of the freeboard space must be limited to less than an optimum value to reduce heat losses and maintain high inlet temperatures.
However, this limitation of the freeboard space height is not without disadvantages. For example, it curtails the residence time of the gases in the freeboard space resulting in less than optimum reaction efficiency. Also, it is inconsistent with the design goal of maintaining the freeboard space at temperatures at, above, or near operating bed temperatures to kinetically promote more complete reactions above the bed. Further, it promotes a maldistribution of the gaseous products of combustion which renders the latter excessively rich in carbon monoxide and hydrocarbons resulting in incomplete combustion.